Proper use of Devnull

[Francisco Vila]

Hello all,

I'm trying to typeset a song that has two lyrics with different melismata in the same melody.
I've found that the Devnull context may help, but I don't know why the lyrics associated to it appears with a slight displacement to the right (see attached PNG).

 % \version "2.11.32"

 c'1 }
two = { d'1 }
 { One }
twoLyrics = \lyricmode { Two }

\score {

<<
\new Voice { \one } \addlyrics { \oneLyrics }
\new Devnull = "hidden" { \two }                % \addlyrics { \twoLyrics }
\new Lyrics \lyricsto hidden { \twoLyrics }
>>
}

%%%%%%%%%%%%%%%%
From my limited knowledge it appears to be in voiceTwo, how is it forced to be voiceOne?

Also, if I uncomment the \addlyrics of the hidden part (and comment out the third line instead), then the hidden staff gets printed on its own staff (and properly aligned as a voiceOne). Why?

I'd thank a clue for learning it by myself, but maybe the manual is too terse in this matter. 
Thank you!
-- 
Francisco Vila. Badajoz (Spain)
http://www.paconet.org

devnull.png
Description: PNG image